1. Field of the Invention
The present invention relates to radio frequency transmission and reception circuits and radio frequency mixers, and more particularly to an apparatus for mixing intermediate radio, or other very high frequency signals with local oscillator signals in a double-balanced ring mixer on a planar substrate. The invention further relates to a ring-type double-balanced mixer for performing very high radio frequency mixing in a uniplanar monolithic integrated circuit.
2. Related Technical Art
A variety of Radio Frequency (RF) mixers have been developed to provide facility for combining a local reference oscillator output with either an intermediate frequency source or a desired radio frequency source for either up or down conversion. Mixers form the key link between antennas and associated processing or decoding circuits. In many applications, such as for advanced Monolithic Microwave Integrated Circuits (MMICs), the desire is to greatly reduce the size of mixers and related processing components to meet volumetric limitations otherwise addressed by MMIC elements and to also minimize power consumption.
One mixer configuration finding use in planar applications is the ring Double Balanced Mixer (DBM) which allows more flexibility in component interconnection. An example of this type of mixer is found in the article "Broadband Double Balanced Mixer/Modulators" by R. B. Mouw and S. M. Fukuchi, published in the Microwave Journal, pages 133-134, March 1969. Currently, most MMIC type DBMs utilize Field-Effect Transistors (FETs) and lumped-element baluns due to the difficulty in realizing a microwave balun to feed a planar ring of four Schottky diodes. Unfortunately, this type of mixer usually exhibits a narrow bandwidth due to elaborate matching requirements and is also relatively unstable due to temperature variations.
To create a broadband mixing structure requires the use of active baluns having several FETs in a distributed configuration. This configuration is generally large in size, compared to conventional MMIC components, and requires large DC power supplies. FET active baluns also introduce additional noise into MMIC double-balanced mixers which degrades their performance.
Current designs for passive planar double-balanced mixers also require fabricating the Schottky diodes and other circuit elements on both sides of a support/base substrate. The assembly is then inserted into a waveguide channel for operation. This type of construction makes this type of mixer unsuitable for uniplanar or true monolithic integrated circuit applications.
What is needed is an apparatus or technique for reducing the areal, packaging, and power requirements for a double-balanced RF mixer. It would be extremely advantageous if the apparatus can be manufactured using known monolithic circuit fabrication techniques such as employed in conventional MMIC applications. The apparatus should provide low loss, MMIC compatible operation.